linux-kernel - Re: [PATCH v4 6/7] sched: add function nr_running_cpu to expose number of tasks running on cpu

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Date:	Tue, 15 Jul 2014 21:03:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S.Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Chandramouli Narayanan <mouli@...ux.intel.com>,
	Vinodh Gopal <vinodh.gopal@...el.com>,
	James Guilford <james.guilford@...el.com>,
	Wajdi Feghali <wajdi.k.feghali@...el.com>,
	Jussi Kivilinna <jussi.kivilinna@....fi>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/7] sched: add function nr_running_cpu to expose
 number of tasks running on cpu

On Tue, Jul 15, 2014 at 08:06:55PM +0200, Mike Galbraith wrote:
> On Tue, 2014-07-15 at 16:53 +0200, Peter Zijlstra wrote: 
> > On Tue, Jul 15, 2014 at 04:45:25PM +0200, Mike Galbraith wrote:
> > > 
> > > 3.0.101-default        3.753363 usecs/loop -- avg 3.770737 530.4 KHz   1.000
> > > 3.14.10-default        4.145348 usecs/loop -- avg 4.139987 483.1 KHz    .910     1.000
> > > 3.15.4-default         4.355594 usecs/loop -- avg 4.351961 459.6 KHz    .866      .951    1.000
> > > 3.16.0-default         4.537279 usecs/loop -- avg 4.543532 440.2 KHz    .829      .911     .957
> > > 
> > > 3.0.101-smp            3.692377 usecs/loop -- avg 3.690774 541.9 KHz   1.000
> > > 3.14.10-smp            4.010009 usecs/loop -- avg 4.009019 498.9 KHz    .920
> > > 3.15.4-smp             3.882398 usecs/loop -- avg 3.884095 514.9 KHz    .950
> > > 3.16.0-master          4.061003 usecs/loop -- avg 4.058244 492.8 KHz    .909
> > 
> > Urgh,.. I need to go fix that :/
> 
> I'm poking about.  It's not just one thing 'course, just lots of change
> adding up to less than wonderful.  Idle changes are costing some, for
> obese config, avg goop.  The select_next_task() reorganization appears
> to be costing, but eyeballing, I can see no excuse for that at all.

How is the idle stuff costing, cpu-affine pipe-test should pretty much
peg a cpu at 100%, right? Or did I mis-understand and are you running a
loose pipe-test?

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